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Would sort out the slow ones I suppose.
You could go down to the local bridge one night and string a net up and spook a few out.

Get in touch with the local pigeon racing club. I use to get 20-40 pigeons once a week of a guy in Blenheim. I used them from a release trap, also just put my dog in a sit and let them go one at a...

Here you go https://www.maintracgroup.com/collections/alphachloralose-bird-poison

There is a poison you can use for pigeons that puts them to sleep, then you can "release" them later.